1. Field of the Invention
The present invention relates to a sight controllable display device that can be visually recognized only by a specific user and to a terminal that comprises the same.
2. Description of the Related Art
Recently, the number of occasions to handle confidential information on terminals has been increasing. The most typical example of such occasions is the use of a financing terminal, and a personal identification number needs to be imputed for using such financing terminal. Further, it has become very often to handle secret information at offices and the like. Furthermore, there have been an increasing number of opportunities to connect to a network with a mobile telecommunication or at a public place due to an advanced radio technology, which has provided us with more convenience. However, it has also increased the chances for the information that needs to be concealed to be checked on a screen.
Under such circumstances described above, there has been a demand for a sight controllable display device (referred to as “display device” hereinafter) that can be viewed only by the user. It is desirable for such display device to have two display modes. A plurality of people can view an image on the screen with a first display mode, which thereby is referred to as an open mode. Meanwhile, only a specific user can view the image with a second display mode, which thereby is referred to as a concealed mode. Examples of such display device may be those disclosed in Japanese Unexamined Patent Publication H05-173127 (Patent Documents 1), Japanese Unexamined Patent Publication H05-323267 (Patent Documents 2), and Japanese Unexamined Patent Publication H06-110403 (Patent Documents 3). Each of the display devices disclosed in Patent Documents 1, 2, and 3 will be described hereinafter.
Patent Document 1 will be described by referring to FIG. 15. In Patent Document 1, a viewer-side polarizing plate 155b of a liquid crystal display device 150 is attached/detached to/from a display panel 152 in accordance with a display mode. By attaching the polarizing plate 155b on the front face of the display panel 152, a plurality of people can view an image on the screen. This corresponds to the open mode. In the mean time, the image becomes unrecognizable when the polarizing plate 155b is detached from the front face of the display panel 152. This concealed image can be viewed only by a specific user who has attached a polarizing plate 155c. This corresponds to the concealed mode.
Patent Document 2 will be described by referring to FIG. 16. In Patent Document 2, a display device 200 is constituted with a backlight 214, polarizing plates 205a, 205b, liquid crystal panels 220, 221, 222, and the like. Display information is supplied to the liquid crystal panel 220. Meanwhile, signals from a random signal generating circuit 223 are supplied to the liquid crystal panels 221 and 222. The screen of the liquid crystal panel 221 is viewed through glasses that are constituted with the liquid crystal panel 222 and the polarizing plate 205b. The signals from the random signal generating circuit 223 are supplied to the liquid crystal panels 221 and 222 simultaneously, so that the display image modulated in the liquid crystal panel 221 is demodulated in the liquid crystal panel 222. Thus, only the user using the above-described glasses can view the display image on the liquid crystal panel 220.
Patent Document 3 will be described by referring to FIG. 17. In Patent Document 3, one-time display scan is completed with two sub-display periods. The sub-display period is constituted with a half the normal display period. A display image is generated in the first half of the two sub-display periods, and an image obtained by inverting the negative and positive of the display image is generated in the latter half of the sub-display periods. The luminous of the two images are leveled, so that a third party cannot recognize the display image on a display panel 302. In the meantime, by using glasses with a shutter 304 and opening the shutter 304 only in the first half of the sub-display periods, only the display image can be seen from the display panel 302. Thus, the display image can be recognized.
However, there are following issues in the display devices disclosed in Patent Documents 1, 2, and 3.
With Patent Document 1, it is necessary to rearrange the polarizing plate physically when switching from the open mode to the concealed mode. Thus, the display modes cannot be switched easily and frequently. In addition, at the time of the concealed mode, a third party other than the viewer can easily recognize the image by the use of the polarizing plate. Like this, Patent Document 1 has an issue in terms of practicability and concealing property.
With Patent Document 2, the display image can be viewed only by those who can obtain the random signals. Thus, the concealing characteristic of Patent Document 2 is more improved compared to that of Patent Document 1. However, like the case of Patent Document 1, it is still necessary to rearrange the polarizing plate on the surface of the liquid crystal panel for the open mode. Therefore, it is also difficult in this case to switch the modes easily and frequently.
With Patent Document 3, the display image can be recognized only by the viewer who has the synchronized shutter. Further, the display image can be viewed without using the shutter when the same images are formed in the first half and latter half of the display periods. However, it is necessary to shorten the one display period for forming the display image. Thus, a high-speed drive system is required in the display device for obtaining images with high definition. Furthermore, display of the image has to be completed in a half the normal period. Therefore, when using a liquid crystal display device, for example, it is necessary to use the one in which the liquid crystal element operates at a high speed. Particularly, when displaying a moving picture, there requires a high-speed transition of the liquid crystal from a halftone display state to a halftone display state. However, the liquid crystal is known to be slow when transiting from the halftone state to the halftone state. Furthermore, currently, a wide view angle liquid crystal display mode is broadly used in a large-scaled display device. For example, an in-plane switching type, a multi-domain vertical orientation type, and the like are broadly used for the wide view angle liquid crystal display mode. In the current liquid crystal elements capable of such wide view angle display, there is no such type that can respond within a half the normal display period. As described above, regarding Patent Document 3, there is a large restriction in the capacity of the display screen and the liquid crystal display mode. Thus, it is difficult to be put into practical use.
The object of the present invention therefore is to provide a display device which can switch the display modes easily, has high concealing characteristic, and can be applied to a current liquid crystal display device easily.
A display device according to the present invention comprises two polarizing plates opposing with each other, a display panel provided between the two polarizing plates, a modulator provided between the display panel and either one of the two polarizing plates, and an observing shutter. The display panel has a function of forming an image by changing transmittance of light that transmits through the two polarizing plates. The modulator has a function of repeating an inversion mode for inverting an image formed on the display panel and a non-inversion mode for not inverting the image. The observing shutter has a function of repeating a translucent mode for transmitting light and a shielding mode for not transmitting the light in connection with an action of the modulator. For example, the observing shutter turns to the shielding mode when the modulator is in the inversion mode and turns to the translucent mode when the modulator is in the non-inversion mode.
Further, the present invention may be structured as follows.
A first aspect of the present invention is a display device that comprises a laminated unit of a display panel and a modulator provided between polarizing plates, wherein there is a period for operating the modulator within one display period of the display panel, and an observing shutter that operates in connection with the modulator operating period is provided. Through employing the first aspect of the present invention, an open mode and a concealed mode can be easily switched by the on/off setting of the modulator. Further, for the display panel, a regular liquid crystal display panel can be used. With this aspect of the invention, only the modulator requires a high-speed operation. Thus, it is possible to use any display panel in terms of definition, response speed, and the view angle performance.
A second aspect of the present invention is the display device according to the first aspect of the invention, wherein the modulator is constituted to be capable of modulating the birefringence or optical rotation property to be added to the incident light. Through employing the second aspect of the invention, a proper modulator can be selected in accordance with the liquid crystal display mode of the display panel. Particularly, in the case where the display panel is a birefringence control liquid crystal type such as an in-plane switching type, a multi-domain vertical orientation type, and an OCB type, it is possible to use the one that controls the birefringence amount for the modulator. Further, it is possible to constitute the modulator to control the optical rotation property. These modulators can all be constituted with a conventionally well-known liquid crystal element.
A third aspect of the present invention is a display device, wherein the modulator is constituted to be capable of modulating the depolarization characteristic of the incident light. A fourth aspect of the present invention is the display device according to the third aspect of the invention, wherein the modulator is constituted with a compound of a liquid crystal and a polymer. It is understood that the modulator of the third aspect of the invention can be constituted also with an element that has the depolarization characteristic. Particularly, it is understood that the modulator can be constituted with a compound of a conventionally well-known liquid crystal and polymer through employing the fourth aspect of the invention. The compound of the liquid crystal and the polymer requires no orientation film and orientation processing, and it can be formed at a lower cost compared to the modulator shown in the second aspect of the invention.
A fifth aspect of the present invention is the display device according to the first to third aspect of the invention, wherein the modulator is operated by generating a sequence of two values or more for controlling the modulation amount of the modulator. The concealing characteristic can be more improved by employing the fifth aspect of the invention. Since the modulator operates in accordance with a specific sequence, only those who use the shutter that is capable of receiving the sequence can recognize the display image.
A sixth aspect of the present invention is the display device according to the first to fourth aspects of the invention, wherein the modulator is divided into a plurality of segments, and changes the segment to perform modulating action or the modulation amount thereof for each modulation period. The concealing characteristic can be more improved by employing the sixth aspect of the invention. By employing this aspect of the invention, it becomes possible to generate a more complicated image by superimposing the modulator pattern image on the display image. In addition, by changing the pattern image to be superimposed through changing the modulator pattern image in time series, still more complicated image can be generated.
A seventh aspect of the present invention is a terminal that comprises the display device of the first to sixth aspect of the invention loaded thereon. By employing the seventh aspect of the invention, highly confidential information and image can be viewed on an arbitrary terminal without worrying about being looked at by others.
With the present invention, it is possible to switch the open mode and the concealed mode easily by the on/off setting of the modulator. Further, a regular liquid crystal display panel can be used for the display panel. That is, only the modulator requires a high-speed operation. Thus, it is possible to use any display panel in terms of definition, response speed, and the view angle performance.